With reference to relevant to research studies, to what extent does genetic inheritance influence behaviour?

You may (should!) remember that one of the key assumptions of the Biological Level of Analysis is that

human behaviour is strongly influenced by our genetic make-up and our genetic inheritance. This means that patterns of behaviour can be inherited.

Once we begin to break this assumption down, however, it becomes more controversial. This page will focus on questions such as:

Which behaviours are influenced more by genes and which are not?

How do genes and the environment interact

What determines whether we will inherit a particular behaviour or condition?

Focus on Command Term - To what extent

﻿Consider the merits or otherwise of an argument or concept. Opinions and conclusions should be presented clearly and supported with appropriate evidence and sound argument(s). ﻿

﻿Level 3﻿

﻿Background to genetic research: family, twin and adoption studies﻿

﻿Genetic studies will often look at families and twins. This is because we know precisely how what proportion of genes are likely to be shared between people (identical twins will share 100% of their genes, whereas siblings and non-identical twins will share 50%, for example). If one person in a family or twin pair develops a psychological condition, researchers may look at how likely it is for other people in their related group to also develop it. For example, if one person in a pair of twins has schizophrenia, researchers may want to establish the probability that the other twin will also be schizophrenic – this is called the concordance rate.

The picture on the right is taken from a National Geographic feature with fantastic photo portraits of identical twins. View it here.

﻿The direction of causality - a major issue in genetic research﻿

﻿As you can see from the evaluation issues above, it is sometimes hard to tell what causes what in psychological illness. We are left with a 'chicken and egg' scenario, where we know that things have changed, but do not know exactly what has caused the change.

This is a major problem for lots of research. For example, if we find that a person with a condition has unusual neurotransmitter levels (see below), we don't know if the condition caused the neurotransmitter levels or if the neurotransmitter levels caused the condition! It is therefore an evaluation issue that you can use repeatedly in your essays, providing you understand it and link it clearly to the topic you have been asked about!﻿

﻿This picture is also very relevant to the nature/nurture debate...﻿

The difficulties with studying genetics...

﻿Genetic studies are often able to provide strong evidence for a genetic basis in many conditions, especially between very closely related individuals such as MZ (monozygotic/identical) tiwns.﻿﻿However, concordance rates are never 100% and therefore this data does not exclude environmental input.﻿

High concordance rates in MZ twins may be explained by the fact that they tend to be treated more similarly than DZ twins and this greater environmental similarity, rather than genetic similarity, may be responsible for the higher level of concordance than in DZ twins.﻿

﻿However, it could be argued that MZ twins elicit more similar treatment from their parents than do DZ twins. This suggests that the greater genetic similarity of identical twins may be a cause, rather than an effect of their more similar parental treatment. Again – what is the direction of the relationship?

These points illustrate that the cause of any psychological condition or behaviour is not wholly genetic. Inheritance may put people at risk but life events and environmental inputs may trigger the actual onset of the behaviour.

Most behaviours will be the result of the interaction of a large number of genes, and at present we do not know precisely which ones are active or how they interact with each other.

﻿Genetic explanations are reductionist, as they reduce complex conditions to the supposed activity of just a small number of genes. This seems too simplistic.

Genetic explanations are also deterministic. They seem to offer the sufferer no hope of controlling the condition themselves, as we cannot consciously control the activity of our genes.﻿

We don't know what causes what in schizophrenia (or any other psychological condition)... The red arrows are possible causes, but we don't know which one is the most important in forming the condition.

﻿Untangling causality - Adoption studies﻿

﻿The notion that genetic factors are important in producing schizophrenia is supported by adoption studies. One approach is to look at adoptees with schizophrenia compared with their biological and adoptive parents. See the video above for more.﻿

﻿Study 1 - Bouchard et al (1990) - The Minnesota Twin Study﻿

﻿Intelligence is a topic which never fails to create debate, and the debate about the extent to which it is heritable (passed on in families) or more due to environmental influences has been raging for hundreds of years. Bouchard et al (1990) wanted to determine how much of intelligence can be attributed to genetics and how much to the environment. Their full research paper (which contains results for a number of other variables as well as intelligence can be read here. ﻿

Bouchard's results. MZT = monozygotic together. MZA = MZ apart etc

﻿Bouchard et al conducted a longitudinal study (they began the study in 1979 and it is still going), following over 100 sets of MZ twins and triplets raised apart. The concordance rates between these sets of twins could be compared to those of identical twins raised together and DZ dizygotic (fraternal) twins raised together from around the world to see the relative effect of nature and nurture on a large range of different characteristics, including intelligence.

Researchers gave them approximately 50 hours of psychological and physiological testing. To measure IQ a number of different tests were used, including the WAIS and an adapted Raven test. For more on intelligence and intelligence testing, see the Intelligence page.

Results

Concordance rates for IQ were 86% for MZ twins reared together (compared to an 87% rate for the same person doing the test twice)

Similarity rates between MZ twins reared apart was approximately 76%

Bouchard determined a heritability estimate of 70% of intelligence attributed to genetics, and 30% to other factors. ﻿

﻿Connecting the study to the question﻿

﻿This study relates to the effect of genetics on behaviour as the concordance rate between twins shows that their behaviour was affected mostly (70%) by genetics, rather than the environment, where the other 30% may be attributed to other factors in the surrounding environment.

Of course, there are some evaluation issues with the experiment which may affect our confidence in its conclusions...﻿

- Relied on media coverage to recruit participants- Ethical concerns with the way twins were reunited- Frequency of contact between twins prior to study not controlled.- 'Equal environment assumption' - twins reared together may not have experienced the same environment.

- Size of the study means it is more generalisable- Nature of sample - cross cultural- Mean age of participants: 41 years, as opposed to previous studies with adolescents- Longitudinal study

﻿The great 'heritability' debate/misunderstanding﻿

﻿﻿Heritability seems like a fairly simple idea... but it is actually a complex and often hugely controversial topic. A good example of this are the controversial comments about IQ and genetics made by British politician Boris Johnson. Read more about this controversy here and the backlash here and in this video

It is easy to see a figure such as "70% heritability" such as from the Bouchard study and to think that this means that the environment will have very little effect on IQ... but this is UNTRUE! Height is very heritable... but if you grow up malnourished then this trait won't show up, regardless of the genes you have. IQ is the same - the environmental influence is still crucial. Also heritability is a population statistic - it's an average across lots of people. Some people's IQ may be affected less by their genes, and some people's more. You can't therefore say for certain the exact amount that any one person's IQ is heritable.﻿It is important to show that you are aware of these nuances in your essay!

Assignment 1 - Summarise Bouchard's findings

WITHOUT looking back at your notes, try to write down:

Three findings of the Bouchard et al study which support the idea that genes affect IQ

Three problems with the research which mean that we have to be cautious with the findings.

The causes of depression are numerous, and vary a great deal from person to person. However, given that there is a tendency for depression to run in families (using research methods such as family and twin studies as described above), there has long been the suspicion that at least a part of the cause of depression is genetic. Once this question has been answered, of course, the next question is which genes might be responsible? Again, it is highly unlikely that such a complex and varying condition will only have one gene associated with it, but researchers have begun to identify some genes which could play a role in the process. Caspi et al (2003) was one of these studies, looking at the effect of possessing different types (alleles) of the 5-HTT gene.

﻿Genes and alleles... a recap!﻿

﻿Just in case you've forgotten your GCSE Biology... here is a reminder of a few key terms for this study.

Gene - a length of DNA which codes for the production of a protein

We have two sets of each gene in our bodies (one from each parent). Different versions of the same gene are called alleles (so for example, in the genes which code for eye colour one allele may code for brown eyes, and another allele may code for blue eyes).﻿

5-HTT alleles - long and short

In the 5-HTT gene, the two alleles which were studied by Caspi were known as the 'long' and 'short' alleles. In the human population, the frequency of the long allele of 5-HTT is about 57% that of the short allele is 43% (OMIM, 2003). These alleles coded for a protein which acts as a serotonin transporter (responsible for taking serotonin back up from the synapse into the neuron). See the picture below for a more detailed explanation. The 'long' allele was thought to lead to the production of a greater number of serotonin transporters, giving greater control over the levels of serotonin in the synapse.

A picture showing the different effects of S and L alleles for serotonin transporters at the synapse. The brain scans also illustrate decreased communication between the amygdala and perigenual anterior cingulate cortex for S allele individuals compared to L allele individuals.

﻿Caspi's method﻿

﻿As well as determining the 5HTT alleles for each of their 847 subjects (s/s = 147, s/l = 435, l/l = 265), when the subjects were 26 years old, the researchers evaluated:

Whether or not the subjects had experienced one or multiple stressful events since their 21st birthday. This was done using a life-history calendar.

Thirty percent of the study members experienced no stressful life events; 25% experienced one event; 20%,two events; 11%, three events; and 15%, four or more events.

2. Whether or not they developed depression in the past year (using an official Diagnostic Interview Schedule for depression)

Caspi's results

Depression after stress was then related to the subjects' genotypes. The results suggested that:

Individuals having two short forms (s/s) of the gene were most likely to be depressed after stressful events

Individuals with one long and one short (s/l) form were moderately likely to be depressed

Those with two long alleles (l/l) typically responded as if no stressful events had occurred.

Assignment 2 - Caspi's conclusions

Caspi et al wrote the following as a part of their conclusions. What point are they trying to make? Try to summarise their conclusions in your own words.

Much genetic research has been guided by the assumption that genes cause diseases, but the expectation that direct paths will be found from gene to disease has not proven fruitful for complex psychiatric disorders. Our findings of Gene/Environment interaction for the 5-HTT gene, point to a different, evolutionary model. This model assumes that genetic variants maintained at high prevalence in the population probably act to promote organisms’ resistance to environmental pathogens. We extend the concept of environmental pathogens to include traumatic, stressful life experiences and propose that the effects of genes may be uncovered when such pathogens are measured (in naturalistic studies) or manipulated (in experimental studies).

Evaluating Caspi et al

Caspi et al provide strong evidence for the need to look at the interaction of nature and nurture (or of genes and the environment) in examining human behaviour. However, there is some debate about exactly what their results seem to show.

On the one hand, this seems to be clear evidence of a genetic factor in the development of depression. People with short alleles were the most likely to become depressed after stressful life events.

On the other hand, since
so many people carry the s allele (almost half the population), it is hard to say that in is the gene that
made the difference. Maybe
it was the environmental factors (stressful events) that caused the depression. Certainly there is not a cause-effect relationship between the genes and the condition.

﻿What conclusions can we draw from genetic studies?﻿

﻿Clearly genetic studies have the potential to revolutionise our understanding of psychology and who we are. However, we are still at an early stage in this journey, and we must take care to overcome some significant remaining hurdles if we are to be confident in drawing conclusions from these studies. For example...

What about treatments? Finding genes that are involved in certain behaviours or conditions suggests that we should also be able to find treatments for them (e.g. a 'cure' for depression or for low IQ)... but this is not the case. Changing genes in living cells is not feasible at the moment, and in actual fact maybe genes aren't the right level to be looking for treatments at. Maybe we should work on finding neurochemical treatments instead.

Genes and the environment have a bi-directional relationship in creating behaviour. Genes affect the environments we seek out and our reactions to them. However, the environment also affects how our genes work! Genes become more or less active in different environments (this is something that we have only begun to discover in the last few years - previously it was assumed that gene expression remained constant throughout our lives).

We may know the gene... but we don't understand the process! Identifying the genes related to certain traits is one thing, but knowing exactly HOW the genes have their affect and how the processes work is another thing. At the moment we understand very few of these processes clearly. For example... we don't really know how having more 5HTT receptors (which should lead to less serotonin at the synapse) seems to protect against depression, or why SSRI drugs (which lead to MORE serotonin in the synapse) ALSO seem to help depression! Contradictory evidence like this must be evaluated further before any better treatments can be developed.

Genes are not behaviours. As we will see again in the evolutionary psychology page next... possessing a gene which makes you vulnerable to a certain condition does not necessarily mean that you will display the behaviour. GENES ARE NOT DESTINY! Therefore it is impossible to draw clear links between genetics and behaviour, without a thorough understanding of the environment in which those genes are being expressed.

Triangulating evidence

Although we have not looked at any genetic evidence in previous parts of the course, this does not meant that it is totally irrelevant. The nature/nurture debate has still been mentioned in a number of different areas, and studies which show an effect of the environment can clearly be used here to illustrate how genetics are not the only factor in behaviour.

For example:The case study of Genie can be used to illustrate the importance of the environment in normal behaviour. There was also the question about whether Genie's condition might have been partly innate/genetic to start with, or whether it was entirely due to the environment, which is clearly also relelvant here.

Assignment 4 - Section A question

Re-read the information above and then answer the following question from memory:

Explain one way in which genetics can influence behaviour (8)

22 mark Section B essay question

All sections with a Level 3 command term can be assessed in a 22 mark essay (remember that a learning objective with a 22 mark command term could also come up as an 8 mark question, but not vice versa). Although any Level 3 command term could be asked, we'll concentrate on the one given in the learning objective, so the question is

With reference to relevant to research studies, to what extent does genetic inheritance influence behaviour? (22)

You will need to plan an essay which will be about 2-3 sides of A4 long, including a detailed focus on the command term.

The marking criteria are below. ALWAYS refer to these before you begin to plan your essay. It is crucial that you know what the examiners are looking for so that you can write exactly what is needed for top marks!

Planning a great 22 mark question

KNOW THE COMMAND TERM! This is absolutely crucial! A different command term requires a different style of essay, so you need to tailor what you write to the question. You will still be able to use the same pieces of information, but how you use them may vary.

PLAN PLAN PLAN! Every year the examiners' comments mention that essays which are clearly planned score the best marks. FOLLOW THEIR ADVICE! Don't be afraid to spend up to 10 minutes in an exam planning your essay (and longer earlier in the year when are learning and practising).

USE EVIDENCE! You have 2 detailed studies here to use, but you should also look to find triangulating evidence using other experimental methods or from other areas of the syllabus

EVALUATE! You must evaluate the studies you present. Evaluating means talking about the strengths and weaknesses of the study as well as the strengths and weaknesses of the level of analysis as a whole with reference to the question (e.g. reductionist explanation of genetics in some behaviour)